I might be a snob

You're the second to have posted as such in the last couple of days, Galileo would be wondering why he bothered to climb the Pisa tower!

 

Acceleration due to gravity is irrespective of weight.

 

The only theoretical gain would be in overcoming friction (negligible) and rolling resistance (low). Since the additional weight as a proportion of the total weight of bike and rider is very small and acting on such limited gain factors, the total gain is below anything that can be observed by a rider.

I don't believe that's right , Flecc. It would be correct in a vacuum. Gravity accelerates you down the hill until you reach your terminal velocity, at which point your weight component is equal to the air resistance plus the much smaller rolling resisistance. So, if you have two riders of different weight rolling down a hill from a stand-still, they will initially accelerate the same, but quite quickly the net force down the hill (weight component minus air resisistance) will be larger for the heavier rider, so he'll accelerate away from the lighter one and reach a higher terminal speed.

 

It's the same thing with a feather and a feather cast in lead. When dropped off the the leaning tower of Pisa, the lead feather will reach the ground a long time before the feather one.

 

You can find a good explanation of the physics here:

http://penultimates.blogspot.co.uk/2012/08/the-physics-of-cycling-ii-or-why-i-am.html

Yes, as I said, a theoretical gain. My point is that it's not worth mentioning if a rider cannot observe it.

 

N.B. Crossed with Rob's post.

 

Needless to say I agree.

 

I respect anyone who can understand the physics, but that knowledge is useless unless it is properly applied.

flecc is correct. The potential energy is proportional to weight, accecelation is inversely proportional to weight. E-kit weight has no effect on consumption on a round trip.

I don't believe that's right , Flecc. It would be correct in a vacuum. Gravity accelerates you down the hill until you reach your terminal velocity, at which point your weight component is equal to the air resistance plus the much smaller rolling resisistance. So, if you have two riders of different weight rolling down a hill from a stand-still, they will initially accelerate the same, but quite quickly the net force down the hill (weight component minus air resisistance) will be larger for the heavier rider, so he'll accelerate away from the lighter one and reach a higher terminal speed.

 

It's the same thing with a feather and a feather cast in lead. When dropped off the the leaning tower of Pisa, the lead feather will reach the ground a long time before the feather one.

 

 

I have factored for the reality. We are not speaking of rider weight differences which can be very large, up to 50 or more kilos, this is about the gain in weight of the e-bike components as a proportion of total bike and rider weight, which is very small.

 

For that the practical gain is negligible.

My money would be placed on the bigger guy every time:)

I suppose I should have stated my assumptions:

 

The rider being fairly fit for road racing would be more than capable to provide enough energy to exceed assisted speed on the flat and down hill stretches.

If you look at the graph in the link above, a 10% difference in weight makes a significant difference in terminal rolling speed. It looks like about 5 mph down a 5% hill and maybe 10mph down a 10% hill.

My money would be placed on the bigger guy every time:)

 

I agree, but that's not the subject, it was about the downhill effect of weight gain of e-bike components, something I've looked into previously in depth.

 

Across a range of riders, bikes and e-bike weight additions, the median e-bike weight gain is circa 6%. However the weight gain brings increases in rolling resistance and friction, so rounding down the weight gain advantage to 5% is justified.

 

Now look at that in practical circumstances. Can a rider perceive a 5% speed difference between 15 mph and 15.75 mph? Can a rider perceive a gradient difference between 12% and 12.6%? The answers of course are no, and the same goes for that theoretical downhill speed gain from a 5% weight increase. It's so slight a rider will not perceive a gain at the time of riding first his bike down a given hill without e-bike kit and later with e-bike kit.

If you look at the graph in the link above, a 10% difference in weight makes a significant difference in terminal rolling speed. It looks like about 5 mph down a 5% hill and maybe 10mph down a 10% hill.

 

 

I understand that well Dave, but as I've posted above to Shemozzle, the weight gain is much smaller and in practical circumstances will not be perceived. That's why I think it not worth mentioning as a noticeable gain.

 

Of course if we compare it to the gains of streamlined helmets, all-over skin tight lycra, slippery paint finishes and oval spokes it's real enough.

:rolleyes:Don't forget to mention the performance enhancing drugs.

:rolleyes:Don't forget to mention the performance enhancing drugs.

 

Now you are into very big gains, seven Tour de France wins even!

:rolleyes:Don't forget to mention the performance enhancing drugs.

They don't seem to work on me. That's why I use my weight instead.

its not all about weight

 

Danny is one of the lightest riders on the circuit and he seems to do ok.

 

this is worth a watch, if you've not see it before.

 

 

google danny hart champery if the link doesn't work.

Here's the video link for the above KTM post, 10 minutes.

 

That's the full length one, here's the edited

.

.

Edited January 18, 201412 yr by flecc

its not all about weight

 

Danny is one of the lightest riders on the circuit and he seems to do ok.

 

this is worth a watch, if you've not see it before.

 

 

google danny hart champery if the link doesn't work.

 

Hi Colin,

 

I assume it is still Colin, I understood from your opening post that you posed a question how much faster a daily commute would be on an ebike I didn't realise you were talking off road.

Hi, yes sorry - still me.

 

my commute is on road. but I do have lots of offroad options, that I do when its dry.

 

I was just trying to make things a bit clearer on here, there is lots of take of numbers, but no one seemed to have actually done anything to show how much faster or easier things are with an eBike.

 

So we've set about planning a load of things over the coming few months to allow our dealers to actually put some sensible numbers together to give customers real world figures that are actually useful to them.

 

Col.

Here's the video link for the above KTM post, 10 minutes.

 

That's the full length one, here's the edited

.

.

 

thanks flecc. I'll have to have another look at how to post links.

 

Col

thanks flecc. I'll have to have another look at how to post links.

 

Col

 

 

Here you are Col. Heading the reply box are icons, the rectangular 9th one across is shown as "Link" if you hover your mouse pointer over it. Highlight the text you want to be a link, click that icon and then paste the link into the URL box that appears. Click the "Insert" button that's under the URL box and then post the contribution.

ah, yes that makes more sense, thanks... I was using the media option, which just didn't work.

 

will amend my posts above.

 

Thanks

Col

It depends what you are trying to achieve, if it is maximum speed on a journey then surely it just means applying maximum assist at times when the speed is below assist level but if you are looking at efficiency of using the stored energy available from the battery then you need to know what are the most efficient speeds in each gear, for that you would need to know the power curve of the motor.

 

I wouldn't have thought it would not be to difficult to program an extra processor output to illuminate an extra indicator on the display when you are hitting the sweet spot.

Edited January 18, 201412 yr by shemozzle999

Here's the video link for the above KTM post, 10 minutes.

 

That's the full length one, here's the edited

.

.

 

'E's bloody mad, I tell ya!

if you are looking at efficiency of using the stored energy available from the battery then you need to know what are the most efficient speeds in each gear, for that you would need to know the power curve of the motor.

 

This is where systems like the legal speed Panasonic crank unit are at their best, the torque sensing and software combined enforcing optimisation for efficiency. Not ideal for the performance enthusiasts though.

Whilst not commuting I had the chance to do a comparison last week with a local 24 year old club rider/ national road race rider on a training ride he did.

 

It was 36 miles with 2,900 feet of climbing, he did it in 2.42 hrs at an average speed of 13.5 mph, by his own admission he wasn't going for it and did the 6 climbs of a small loop in the big ring. His bike is a light carbon racing bike.

 

Because it was local and not like his usual 60 to 100 mile rides I thought I'd have a go and see how I compared. I packed my spare 300 w/h battery in the pannier and set off with a full 400 w/h battery, I also disabled the speed restrictor. Bear in mind I'm twice his age and not in good health. I doubt very much I was getting any where near his power output.

 

Anyway I did the 36 miles in 1.52 hrs at an average speed of 19.3 mph ! have to say I was quite chuffed with my performance. It would have been a little quicker had my second battery not expired 1 mile before the finishing line. I have a feeling he'll be back out one day to try and beat it and put me back in my place.

ok, just been thought the stats on my Garmin, and here are the results.

 

Bike used was a 2014 KTM Macina Action mountain bike - 29er with Bosch Active drive. It had standard mountain bike tyres.

 

Conditions were similar to the previous day when I'd ridden a standard road race bike home.

 

Homeward bound.

 

Normal Bike: 55.13 minutes. Average Speed of 17.3mph and average heart rate of 152

 

looks like I had a bit more of a headwind when I rode home on Sunday, because last night with the eBike I did.

 

45.25 minutes. Average Speed of 20.8mph, but I had to work harder for it, average heart rate was 163

 

For the ride into work.

 

Normal bike takes 1 hour 13 minutes. average speed of 12.5mph average heart rate of 156

 

eBike took 1 hour exactly, average speed of 14.9 mph with an average heart rate of 158

 

---------------------------

so basically it knocks 10 minutes off each way, using a similar amount of energy. I went pretty hard, keeping my heart rate at about the level I'd normally commute to see the effect.

 

its was only a bit quicker on the climbs... 2 minutes on a 13 minute climb. Because I normally go pretty hard on the climbs. So it looks like most of the time was made up on the slow speed sections where I'm accelerating away from lights etc etc.

 

Personally its made me realise there is little point in road legal e Road Bikes, ie 700c wheels with drop handlebars and skinny tyres. They simple roll to fast that I'd be over the speed for support for so much of the time that it wouldn't be worth having.

 

Having a mountain bike means the riding is more comfortable and more fun and actually a bit safer in traffic. I'm sure if my commute was more stoppy starty, there would be even more advantages.

 

But I was impressed, I've saved essentially 20 minutes off my commute per day, using the same amount of energy. So if I used this bike every day, that would give me 1 hour 40 extra per week of my life at home to do something better then commuting.

 

Or equally I could ease off a bit on the effort I put in, so the ride takes the same amount of time, but I'll be using loads less effort which will mean I'm fresher in the evenings or weekends to go on actual rides.

 

For a quick estimate how much faster on e-bike, this is my calculation:

distance: 15.9 miles (25.59km), elevation: 1165ft (355.1m), total energy required on a crank drive at optimal gear selection: 25.59*6.3 + 355.1*0.465=326.32WH

These are WH at battery (burn) level, transfer yield at 0.8 is built in.

A good cyclist burns 132W, your cycling ability is much higher than this, at nearly double a good cyclist, so I leave your case for later, I just calculate with normal cyclist profile, the Bosch motor burns 511W, on a derestricted Bosch bike, in ideal conditions (no stoppage), your combined power is 643W, it would take you just 30 minutes to complete the journey.

Without GPS information, assuming 10% average gradient on the hills, 3.5km and 22 km flat roads, the climb will take 15 minutes.

On a restricted bike, the flat section takes 52 minutes at 25km/h. On an unrestricted bike, you can do the same flat section in half the time, 30 minutes.

You should be home in 1 hour 7 minutes with a legal bike, 45 minutes with a derestricted Bosch bike.

With a derestricted 8-Fun BPM and a throttle, you can get home in about 45 minutes without pedalling.

In view that most commutes are within 30 minutes and most of it is flat anyway, good cyclists won't benefit from motorisation unless the bike is derestricted.

The main benefit is to arrive fresh, pink and not hot.

Edited January 19, 201412 yr by trex

Can you do the calculation for a Kudos Tornado with BPM restricted to 26.5mph? Lets say 700W from the battery during slow hill-climing.